Merge change 4431 to V8 2.0

src/ia32/macro-assembler-ia32.cc

Index: src/ia32/macro-assembler-ia32.cc
===================================================================
--- src/ia32/macro-assembler-ia32.cc	(revision 4431)
+++ src/ia32/macro-assembler-ia32.cc	(working copy)
@@ -176,7 +176,17 @@
     j(equal, &done);
   }
 
-  if ((offset > 0) && (offset < Page::kMaxHeapObjectSize)) {
+  // The offset is relative to a tagged or untagged HeapObject pointer,
+  // so either offset or offset + kHeapObjectTag must be a
+  // multiple of kPointerSize.
+  ASSERT(IsAligned(offset, kPointerSize) ||
+         IsAligned(offset + kHeapObjectTag, kPointerSize));
+
+  // We use optimized write barrier code if the word being written to is not in
+  // a large object chunk or is in the first page of a large object chunk.
+  // We make sure that an offset is inside the right limits whether it is
+  // tagged or untagged.
+  if ((offset > 0) && (offset < Page::kMaxHeapObjectSize - kHeapObjectTag)) {
     // Compute the bit offset in the remembered set, leave it in 'value'.
     lea(value, Operand(object, offset));
     and_(value, Page::kPageAlignmentMask);